The present disclosure relates to a plunger for a syringe and a pre-filled syringe including the plunger.
In recent years, a pre-filled syringe that is pre-filled with a medicinal solution has been widely used.
Examples of the pre-filled syringe include those with a plunger not pre-mounted on a gasket and to be mounted on the gasket in use, and those with a plunger that is pre-mounted on a gasket.
A pre-filled syringe with a plunger that is mounted on a gasket is manufactured by what is called a vacuum capper method. In the vacuum capper method, a drug (pharmaceutical) is filled inside a barrel that has an opening sealed at a leading end, and the gasket is placed at the opening of the barrel in an atmosphere under reduced pressure (atmosphere under vacuum), and then, the plunger is inserted into the barrel under ordinary pressure, thereby mounting the plunger on the gasket. Preliminarily mounting the plunger makes it difficult to dispose the gasket in the opening of the barrel, so that the aforementioned capping operation is performed with the gasket alone. For this reason, it is common that a subsequent plunger mounting operation is required in a pre-filled syringe. In regard to a pre-filled syringe with a plunger that is not pre-mounted on a gasket, a user performs the operation of mounting the plunger on the gasket in use.
In a typical pre-filled syringe, an external thread and an internal thread are provided in a plunger and a gasket, respectively, and both threads are screwed together so as to form a mounting mechanism.
An example of a pre-filled syringe is disclosed in WO 01/005456 (US 2008-0051728-A1).
WO 01/005456 discloses a plunger for a syringe in which a gasket can be attached to a thread disposed in a leading end of the plunger, while a central axis of a syringe barrel and a central axis of the plunger are simply aligned. The plunger of WO 01/005456 has the leading end formed with a thread 10 to which a gasket 25 provided in a syringe 2 is attached. A pair of ring members 12 and 13 are arranged at an interval at the back (right side in FIG. 1) of the thread 10, and a plurality of wing members 14 are disposed between the ring members 12 and 13. One ring member 12 is disposed in contact with the thread 10 at the leading end of the plunger 1, and the other ring member 13 is apart in the rearward of the ring member 12. The interval between the ring members 12 and 13 is 0.5 mm or more.
In addition, the present applicant has proposed a configuration in JP 2014-87502 A. A plunger 5 disclosed in JP 2014-87502 A is provided with four reinforcement units 54 provided at a leading end of a body section 50. As illustrated in FIGS. 17 to 19, each reinforcement unit 54 includes a plate-like axial reinforcement unit 54a and a circumferential reinforcement unit 54b having a first end jointed with the axial reinforcement unit 54a. The axial reinforcement unit 54a is formed in a slat-like shape extending by a predetermined length perpendicularly from a surface of any one of slats 51a, 51b, 51c, and 51d included in a shaft and perpendicularly from a rear end surface of a flange 56. The axial reinforcement unit 54a is substantially parallel to a central axis of the plunger. It is preferable that the axial reinforcement unit 54a has a one-sixth or one-quarter axial length of the entire length of the shaft (the entire length of the slat). Furthermore, as illustrated in FIG. 18, the axial reinforcement unit 54a has a terminal end (base end) that is chamfered or arched.
The circumferential reinforcement unit 54b is provided at a position slightly closer to the leading end (closer to the flange 56) than to the base end of the axial reinforcement unit. The circumferential reinforcement unit connects the axial reinforcement unit 54a with the opposing shaft and has a first end in a circumferential direction extending from one side surface of the axial reinforcement unit 54a, and a second end reaching the slat that opposes the axial reinforcement unit 54a. The circumferential reinforcement unit also has a bottom surface connected to the slat from which the axial reinforcement unit 54a protrudes. In other words, the circumferential reinforcement unit 54b connects two slats with the axial reinforcement unit 54a adjacent to the circumferential reinforcement unit 54b. In addition, the circumferential reinforcement unit 54b is substantially parallel to the flange 56.
The aforementioned pre-filled syringe is not a limited example of a syringe, and it is often the case that the air inside of a syringe is required to be removed when the syringe is used. In a case in which a syringe is filled with a liquid having high viscosity or in a case in which a large syringe having a large amount of liquid filled is used, it is necessary to apply a large load during this air vent operation. During this air vent operation, particularly, at the time of initially moving a plunger, the plunger tends to incline because of a small portion that enters a barrel, and such inclination may lead to liquid leakage. A syringe filled with a liquid is often used while mounted on a syringe pump. Even in use of this syringe pump, at the time of initially moving a plunger, the plunger tends to incline because of a small portion that enters a barrel, and such inclination may lead to liquid leakage.